INDUSTRIAL A N D EiVGINEERIiVG CHEMISTRY
78
In the “diluted” water there were approximately half as many organisms as in the “concentrated” water, while the dissolved oxygen was also approximately half, Discussion
In dealing with the pollution of a stream the role of reaeration by green organisms must be properly evaluated. If the pollution is not excessive so that the production of oxygen is overbalanced by the consumption, a marked increase in dissolved oxygen will result. With a more heavily polluted stream the dissolved oxygen might show from day to day, when samples are taken in the afternoon, complete saturation leading to erroneous conclusions because the temporary condition in the afternoon is by no means the daily average condition. Moreover, these erroneous results are usually obtained in the spring and especially in July and August with low stream-flow conditions and higher
Vol. 23, No. 1
temperatures. From the reported and other results obtained it is believed that results for dissolved oxygen have been interpreted as meaning far more than was actually warranted. In stream-pollution surveys several more factors must be taken into consideration. From the high pH values obtained during the afternoons the deduction could have been made that either the water was alkaline or that large quantities of strongly alkaline trade wastes had been discharged. Literature Cited Birge and Juday, Wisconsin Geol. Natl. Kist. Survey, Bull. 22 (1911). Butcher, Pentilow, and Woodley, Biochem. J . , 21, 945, 1423 (1927); 22, 1035, 1478 (1928). (3) Duval and Dumarand, Comfit. rend. sac. biol., 89, 398 (1923). (4) Duvaux, Ann. x i . sat., 9, 286 (1889). ( 5 ) Moore, Biochem. J., 4, Nos. 1 and 2 (1908). (6) Saunders, Proc. Cambridge Phil. Soc., 19, 24 (1920). (1)
(2)
Volatilization of Potash from Wyomingite’ S. L. Madorsky FERTILIZER A N D FIXEDN I T R O G E N
INVESTIGATIONS,
BUREAUOF
The large deposits of the potash-bearing mineral, wyomingite, occurring in Wyoming represent a great potential source of agricultural potash depending on the development of commercially feasible extraction methods. From this viewpoint, various lines of research are being pursued in the Bureau of Chemistry and Soils, among which are smelting methods for the volatilization of the potash. Representative samples of Wyomingite containing about 12 per cent potash ( K 2 0 ) were heated in a small electric furnace, alone and mixed in various proportions with calcium carbonate, calcium chloride, calcium fluoride, and sodium chloride. When the rock was heated alone at
C H E M I S T R Y A N D SOILS, W A S H I N G T O S ,
D.
c
1510” C. more than a fourth of the potash was volatilized in 40 minutes. This volatilization was progressively increased by the addition of calcium carbonate, calcium fluoride, sodium chloride, and calcium chloride. The calcium chloride was the most effective promoter and when combined with calcium carbonate induced a 100 per cent volatilization of the potash even below 1200” C. These results indicate that the method proposed at the Bureau of Chemistry and Soils for extracting potash from Wyomingite by some furnace process is chemically quite feasible. The practical realization of economically successful production would seem to depend primarily upon the design of a suitable furnace unit.
..... ...... I
T
HE potash-bearing leucite deposits of Wyoming, known
as Wyomingite, constitute one of the principal potential sources of American potash. The problem of converting this potash into soluble form, available for agricultural purposes, has been the subject of discussion and research for many years, particularly since the war, when our dependence upon foreign potash forced it more vigorously on our attention. The Bureau of Chemistry and Soils of the Department of Agriculture is conducting a series of experiments designed to convert the potash in Wyomingite and similar minerals into soluble form. Some of these experiments are based on the principle of smelting the mineral a t high temperatures, together with suitable reagents and fluxes. The reagents combine with the potash of the rock to form soluble salts which volatilize a t high temperatures and can be collected by means of precipitators. The fluxes combine with the other constituents of the rock to form a fluid slag which is run out of the furnace. The object of this research is to ascertain the relative value of the reagents or promoters in inducing volatilization of potash in such a smelting process and to investigate the effects of time of heating the mixtures and temperature a t which they are heated on the volatilization. 1 Received September 22. 1930. Presented before the Division of Fertilizer Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 t o 12, 1930.
Leucite is a potassium aluminum silicate and is usually represented by the formula KzO.Al208.4Si02. The pure mineral contains about 21.A per cent KzO, but in wyomingite it is mixed with silica and other impurities, so that the potash content is only 10-12 per cent. I n 1901 Rhodin ( 4 ) heated finely ground mixtures of 100 parts feldspar, 53 parts slaked lime, and 40 parts sodium chloride a t 900” C. for 1 hour. He found that from 60 t o 70 per cent of the potash in the feldspar was changed into potassium chloride. The temperature was too low for volatilizing the chloride, but it could be dissolved out from the insoluble mass. I n 1912 Ross (5) heated feldspar with various amounts of calcium carbonate, calcium chloride, and sodium chloride a t 1000-1050° C. Most of the potash in the feldspar60 to 99 per cent-was rendered soluble. Wells ( 6 ) ,in 1916, heated Wyomingite together with calcium carbonate, calcium chloride, and other reagents to a dull-red heat. On heating 1 gram of Wyomingite with 0.3 gram of calcium carbonate only a trace of potash was rendered soluble. On heating 1 gram of Wyomingite with 0 2 , 0.4, and 0.Ggram of calcium chloride, the amounts of potash rendered soluble were 27.3, 59.0, and 73.0 per cent, respectively. I n a series of experiments conducted by Jackson and hIorgan (5)greensand was mixed with various proportions of calcium chloride, calcium carbonate, and sodium chloride,
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1931
and the mixtures were heated to temperatures from 1050' to 1300" C. The potash volatilized from the greensand in one form or another ranged from 0 to 100 per cent, devendinp on the amounts of reaeents used and on the temperature and time of liesting. The materials charred into the kiln for makiw Portland cement contain small amounts of potash, which isvolatilized in the process of heating the charge. Tlie volatilization is probably induced by the calcium carbonate and the potassium con~esoff 8s a carbonate or sulfate. I
Tlio inetliod of addmg chlorides to a blmt-furnace charge for the purpose of inducing a greater volatilization of potash was tried in England by Chance ( I ) , who observed, while studying the flue dust from the blast furnace, that the amount of potassium carbonate in the dust varied considerably, while the amount of potassium chloride remained constant and smaller than that of potassium carbonate. This led him to the idea that the constancy of potassium chloride w&s due to the constancy of chlorine present in the raw charge, and that all the chlorine was volatilized in the form of potassium or sodium chloride, the ratio between the two salts in the dust also being almost constant-namely, 85 to 90 per cent KCl and 10 to 15 per cent NaCl. By adding a sufficient amount of sodium chloride to the raw charge, Chance wa.9 able to volatilize all the potash present in the charge and to collect it as potassium chloride. Experimental Method and Apparatus The Wyomingite used in this series of experiments was cqllected from various parts of a pile of about one carload size. I t h a d the following composition: 70
% SiOl K*0 AiiOa
PeaMz MgO
51.34 12.76 11.68 4.90 6.92
ChO I'Oa
'Tion NarO
5.07 1.97 2.12 1.42
It-was ground to pass through a 100-mesh screen and dried in-an oven a t 140' C. for 15 hours. A 0.5-gram sample
79
was used in each case. The calcium carbonate, calcium chloride, sodium chloride, and calcium fluoride, which were used as pronioters to induce volatilization of potash from the Wyomingite, were of c. P. quality. They were ground t o fine powders and dried in the same way as the Wyomingite. The materials were weighed in a small platinum crucible, 2 cm. diameter and 3 em. high, thoronghly mixed, and kept in an oven at 140' C. until the crucible was ready to go into the furnace. The iiirnace (Figures 1 and 2) consisted of an alundum tube 2.5 cm. inside diameter and 25 em. long about which a platinum wire was wound, snrrounded by an ahindum tube of 11 em. outside diameter wound with nichrome wire. I n all runs the time of beating was 40 minutes, reckoned beginning with the fifth minute after the crucible was lowered into the furnace. Temperature readings were taken every 5 minutes. The temperature usually fluctuated a few degrees one way or the other from 1510' C., but the average temperature was 1510" C. The Pt-Pt Rh thermocouple was calibrated up to 1000° C. against a standard couple of t.he Bureau of Standards. Analvsis for residual notash was made in tho same crucible in whi& the material 68s heated. The amount volatilized v a s then calculated as the difference between the original KiO in the sample and the residual potash. The method oi analysis consisted in dissolving the sample by means of hydrofluoric and sulfuric acids, precipitating the potassium
Figme 2-Cross Section of Furnace
as potassium sodium cobaltinitrite, and then analyzing for nitrogen by the Kjeldahl method. Whm the samples were heated above about 1200° C., they fused to a glassy mass. It was found difficult to dissolve this glass with acids, but this difficulty was overcome by allowing the sample to stand covered with hydrofluoric acid for 24 to 48 hours. Volatilization without Use of IteaQenta The results of volatilization of potash by heating alone are shown in Table I. Column 4 shows the loss in weight due to volatilization of potash as shown by analysis. It is assumed that the potassiom left the sample as potash. Column 5 shows the actual loss in weight as determined by weighing crucible and material before and after heating in the furnace.
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80
Vol. 23, No. 1
&added
Y 1
zot IO -
-1
1
Effect of adding vanbus amounfs of CaCh fo d?ff mixtures of leucite and CaCO.,. Samples were heated
I
I
0:
I
1
I
I
0.5
Pofash epul'vafenf
/. 5
4 Ca&
1
2 added
Figure 4
potash of the wyomingite is volatilized together with the potassium chloride, it is found that the actual losses in weight determined by weighing the samples before and after heating in the electric furnace are on the average greater by 14.5 mg., or by 2.3 per cent of the total original weight of the samples. It is probable that some of the potash volatilizes as K20, then reacts with gaseous sodium chloride. This would allow a larger portion of sodium chloride to leave the crucible, which would account for the larger actual loss, not accounted for otherwise. 16 17 18 19 24 25
25.63 30.05 26.05 28.60 29.15 29.39 28.18
0.5000 0.5000 0.5000 0.5000 0.5000 0.5000
Average
16.4 19.2 16.6 18.3 18.6 18.8
18.0
16.5 16.4 15.9 16.5 16.9 16.5 16.5
+o.
1 -2.8 -0.7 -1.8 -1.7 -2.3 -1.5
0 0 -0.6 -0.1 -0.4 -0 3 -0.5 -0.3
Table 11-Effect
EXPT.
of S o d i u m Chloride on Volatilization of Potash NaCI-K*O Kz0 NaCl EQUIVALENT VOLATILIZED Gvam
Effect of Sodium Chloride
The reaction between sodium chloride and the potash in the Wyomingite takes place according to the following equation: KzO
+ 2NaC1 = 2KC1 + NazO 361
+ 823
873
+ 415
This reaction is exothermic and the amount of heat liberated is 104 kilojoules. The potassium chloride formed comes off as a vapor a t high temperatures. Jackson and Morgan (S), studying the vapor pressure of potassium chloride a t various temperatures, found it to be 40.4 mm. at 1100" C. At 1200", 1300", 1400", and 1500" C. the vapor pressure is 94.4, 202.0, 404.0, and 760 mm., respectively. Since in the present experiments the temperature was in most cases 1510" C., it is to be expected that whatever potassium chloride formed in this reaction was volatilized from the crucible, so that the analysis of residual potash represents that part of potash which has not reacted with the promoter. Since the Wyomingite contained 12.76 per cent K10, the chemical equivalent of sodium chloride to react with this potash is 0.0792 gram for 0.5 gram of Wyomingite. Table I1 shows the results of these experiments. Assuming that potassium is volatilized in the form of potassium chloride and that any excess of sodium chloride not reacting with the
Figure 3 shows graphically change of volatilization of potash with the amount of sodium chloride used. At first the curve rises slowly, up to the addition of 0.5 potash equivalent of sodium chloride. This can be explained on the ground that when the crucible is lowered into the furnace at a high temperature of 1510" C., a certain amount of sodium chloride volatilizes before the reaction with the potash takes place. When the amount of sodium chloride in the sample is small, most of it volatilizes in the first few minutes, before the mass melts completely, so that its effect on potash volatilization is very small. As the proportion of sodium chloride is increased, more of it remains to react with the potash. When more than a 0.5-gram potash equivalent of sodium chloride is added, the effect of potash volatilization becomes more noticeable and rises regularly. Effect of Calcium Chloride
Calcium chloride acts much like sodium chloride in inducing volatilization of potash from Wyomingite. The reaction can be expressed by the equation:
+ CaCl2 = 2KC1 f
K20
361
+ 798.
CaO
873 f 635
I S D U S T R I A L A1-D ESGISEER12VG CHEJIISTRY
January, 1931
The reaction is exothermic a i d the amount of heat liberated is 394 kilojoules. A potash equivalent of calcium chloride for 0.5 gram Wyomingite is 0.0752 gram. Table 111 shows the result of these experiments. It is assumed here again that the potassium of the Wyomingite leaves the crucible as potassium chloride and that the excess calcium chloride not reacting with potash volatilizes along with the potassium chloride, without decomposition. The actual losses are greater than the losses calculated on the above assumption, on the average by 1.3 mg., or by 0.3 per cent of the total original weight of the samples. There is also the possibility of some of the potassium coming off as potash and then reacting with calcium chloride. HoTvever, the agreement between the calculated losses and the actual losses is quite good. Table 111-Effect
EXPT.
of Calcium Chloride on Volatilization of Potash CaC12-Kz0 EQUIVALENT
CaClz Gram
Kz0 \'OLATILIZED
81
are all positive and rise steadily with increase of promoter. This is unlike the case when sodium and calcium chlorides were used as promoters. I n Figure 3 the effect of calcium fluoride on volatilization of potash is shown graphically. Table IV-Effect
of Calcium Fluoride on the Volatilization of Potash CaFrKzO Kz0 CaFz EQUIVALENT VOLATILIZED Gram 76 0.0266 0.50 32.60 0.0529 1.00 36.68 0 0661 1.25 40.51 0.0794 1.50 56.66 0.10%3 2.00 57.37 0.1587 3.00 58.14
EXPT. 26 27 49 28 29
30
It will be noticed that a t first the curve rises steadily u p to one potash equivalent of calcium chloride, when the T-olatilization is 36.68 per cent. The curve then suddenly jumps up to 56.66 per cent volatilization a t 1.5 equivalents. From this point on the curve is almost horizontal and further additions of promoter do not promote volatilzation much. The steady rise of a positive difference between
In Figure 3 the effect of calcium chloride on volatilization of potash is shown graphically. It will be noticed that here, as in the case of sodium chloride, the effect on volatilization is a t first inappreciable until 0.5 an equivalent of calcium chloride is added. ilt this point the volatilization is 30.33 per cent, which is only 2.15 per cent more than volatilization from leucite alone without promoters. This might be explained on the same ground as in the case where sodium chloride is the promoter. The trend of this curve shoirs that further additions of calcium chloride will not help volatilization appreciably. On comparing the calcium chloride and sodium chloride curl-es it will be observed that with small amounts of promoter sodium chloride is more effective than calcium chloride. but as the amounts increase above 1 equivalent calcium chloride becomes more effective than sodium chloride. This is in agreement with the observation made by Ross ( 5 ) ,mho states, in the case of potash volatilization from feldspar, that CaCh "is somewhat more effective than XaCl in bringing about complete decomposition of the feldspar, but when limited amounts of the reagents are used, a somewhat larger amount of the potash is rendered soluble with the use of iL'aC1 than with CaCl?."
j Effect of add!iig various amounts of CaCO, t o different
I
mixtures of leucite and CaCl,. In every rase sampies were a f f5IO'C for 45 rntn.
, heated
1
Effect of Calcium Fluoride Calcium fluoride differs from calcium chloride and sodium chloride in that it melts a t a much higher temperature and its vapor pressure a t 1510" C. is much lower, so that little of it will volatilize. The reaction between calcium fluoride and potash takes place according to the following equation: KzO 361
, 20
25
+ CaFl = 2KF + CaO +
1198
1122
+ 635
The reaction is exothermic and the amount of heat liberated is 198 kilojoules. The potash equivalent of calcium fluoride for 0.5 gram Wyomingite is 0.0592 gram. Table I V shows the results of these experiments. It is assumed here that potassium leaves the crucible in the form of potassium fluoride and that the excess calcium fluoride does not volatilize. The differences between total losses calculated on the basis of analysis of residual potash in the crucible and those found by weighing crucible and material before and after heating
.50
75g CaCO,
Figure 5
calculated and actual loss in weight of the sample andzthe sudden jump in the curve seem to indicate a peculiar behavior for this promoter. The only plausible explanation seems to be that a t high temperatures calcium fluoride would have a tendency to react with silica, according to the following equation : 2CaF2
+ Si02 = 2Ca0 + SiFc
Silicon tetrafluoride is a gas and will leave the crucible, Therefore, when assuming that the only substance leaving
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
82
the crucible is potassium fluoride, the differences between these calculated losses and actual losses become greater, and a.re positive, as more calcium- fluoride is mixed with the Wyomingite. Effect of Calcium Carbonate
The reaction between calcium carbonate and potash of the wyomingite takes place according to the following equation: K2O
+ CaCOs = K2COa + CaO
361 f 1209
1151 f 635
The reaction is exothermic and the amount of heat liberated is 216 kilojoules. The amounts of calcium carbonate used here were not considered from the point of view of potash equivalents. Table V shows the results of these experiments. It is assumed here that potassium leaves the crucible as potassium carbonate and that the only other substance escap-
sodium chloride was added in the amount of 0.1 part to 1 part of greensand and 1 part of CaC03, the volatilization in 15 minutes, even a t 1200O C., was 91 per cent (run 158). Similarly, when 0.09 part of calcium chloride was added to 1 part greensand and 1 part calcium carbonate, and the mixture heated for 15 minutes a t 1170" C., volatilization of potash was 80 per cent (run l65?. Effect of Calcium Carbonate and Calcium Chloride
From the work of Ross ( 5 ) , Jackson and Morgan ( 3 ) , and others on feldspar and greensand, it appears that the best results can be obtained from a combination of calcium carbonate or lime and a halogen promoter, such as calcium or sodium chloride. I n view of this fact and also because in a smelting process limestone would have to be added to the charge to make a freely running slag, a series of experiments was conducted in which calcium carbonate and calcium chloride were used together with the Wyomingite. Various amounts of calcium chloride were added to different mixtures of leucite and calcium carbonate as indicated in Table VI. As before, it is assumed here that the potassium volatilizes as potassium chloride, that any excess calcium chloride volatilises together with the potassium chloride, and that all the carbon dioxide leaves the crucible. The actual losses are greater than the calculated losses, on the average by 4.5 mg. T a b l e VI-Effect
EXPT.
Effect of fime o n volafilization
of K20 In every case a m i x t u r e of 0.Sg leucite, 059 CaCO, and one K,O equivalenf of c h l o r i d e were heated af 1510 OC
20
I
Vol. 23, No. 1
of C a l c i u m Carbonate a n d C a l c i u m Chloride on Volatilization of P o t a s h CaCOa
CaClz
Gram
Gram
CaClrKZO K2O EQUIVALENT VOLATILIZED
% 0.5 1.0 1.5 2.0 0.5 1.0 1.0 1.5 2.0 0.5 1.0
36 37 9 10 45 5 55 39 38 56 47
67.24 86.28 96.79 98.12 73.20 95.29 94.75 100.00 100.00 85.81 99.84
I
10 -
I
0
I0
ZD
a0
40
50
60
70
I
I
80
90
I00
120
IZD
T i m e - mtnufes Figure 6
ing is carbon dioxide. It is also assumed that all the excess calcium carbonate present decomposes into lime and carbon dioxide. The calculated losses are here in fairly good agreement with the actual losses, as determined by weighing the samples before and after heating, the difference being only about 0.8 per cent of the total original weight of samples. T a b l e V-Effect
EXPT. 2; 15 12
of C a l c i u m Carbonate o n Volatilization of P o t a s h Kz0 CaCOs VOLATILIZED Gram % 0.2500 28.61 30.72 0.5000 0.7500 37.85 1.0000 42.79
The curve for this reagent in Figure 3 shows a slow but steady increase of volatilization of potash with amount of calcium carbonate added. Only about 43 per cent of the potash is volatilized when the ratio of calcium carbonate to Wyomingite is 2 to 1, as read from the upper scale. On the whole, it appears that calcium carbonate is quite inefficient in promoting volatilization of potash. This is in good agreement with the work of Jackson and Morgan (S), who found that when greensand and calcium carbonate in the ratio 1 to 1 ivere heated for 11 minutes a t 1300" C. the amount of potash volatilized was only 7-8 per cent (runs 142 and 144). When
I n Figure 4 the data are plotted as iso-CaC03 curves and in Figure 5 they are plotted as iso-CaClz curves. It is seen that by mixing Wyomingite and calcium carbonate in the ratios of 1 to 0.5, 1 to 1, and 1 to 1.5 and adding to the mixtures 1 to 2 potash equivaletns of calcium chloride a complete removal of potash from Wyomingite can be obtained. Effect of Time on Volatilization of Potash
I n studying the effect of time on potash volatilization, uniform mixtures, consisting of 0.5 gram Wyomingite, 0.5 gram calcium carbonate, and 1 potash equivalent of sodium or calcium chloride, were heated a t 1510' C. Table VI1 shows the results of these runs. From a study of curves in Figure 6 it will be noticed that most of the volatilization takes place in the first 10 minutes. In the case of sodium chloride the amount of potash volatilized in this time is 71.79 per cent and in the case of calcium chloride it is 88.05 per cent. From this point on volatilization increases slowly with time and reaches 99.14 per cent in 120 minutes in the case of both promoters. of T i m e on P o t a s h Volatilization w i t h S o d i u m a n d C a l c i u m Chlorides CaClz AS PROMOTER NaCl AS P R O M O T E R Kz0 Expt. Time volatilized K?? Expt. Time volatilized Min. 70 Min. % 88.05 71.78 41 10 4.4 10 6 20 92.56 76.18 4 20 5 40 95.29 85.11 3 40 55 40 94.75 91.50 1 42 60 97.88 6o 96.96 20 60 40 120 99.14 43 120 99.14 ~. a T w o potash equivalents of NaCl used.
Table VII-Effect
~~
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1931
Table VIII-Variation of Volatilization of Potash w i t h Temperature KzO ACTUAL VOLA- Loss Loss Loss TOTALTOTAL EXPT. TEMP.TILIZED COS CaClt KC1 Loss Loss DIFFERENCE C. % Mg. M E . Mg. Mg. Mg. M g . % of total 58 910 2 2 . 1 0 220 5 8 . 7 2 2 . 3 301.0 234.9 - 6 6 . 1 -6.1 57 1010 3 6 . 1 3 220 4 8 . 0 3 6 . 5 3 0 4 . 5 2 5 6 . 1 - 4 8 . 4 -4.5 51 1110 9 8 . 4 3 220 1 . 2 9 9 . 4 320.6 317.0 - 3 . 6 - 0 . 3 50 1160 9 9 . 1 4 220 0 . 7 100.1 320.8 324.6 3.8 f0.3 52 1210 9 9 . 2 2 220 0 . 6 100.2 3 2 0 . 8 3 2 3 . 8 3.0 +0.3 46 1310 9 4 . 3 5 220 4.2 9 5 . 3 3 1 9 . 5 3 3 0 . 0 +10.5 f 1 . 0 54 1310 9 6 . 0 4 220 1.7 9 8 . 7 320.4 329.4 9 . 0 +o. 8 48 1410 9 9 . 7 2 220 0 . 2 100.7 320.9 328.9 8 . 0 +0.7 S 1410 8 8 . 3 4 220 8.2 8 9 . 2 317.4 330.0 + 1 2 . 6 f l . 1 53 1410 9 9 . 4 5 220 0 . 5 100.4 320.9 335.0 +14.1 f 1 . 3 5 1510 9 5 . 2 9 220 3.5 9 6 . 2 3 1 9 . 7 331.2 + 1 1 . 5 + 1 . 1 55 1510 9 4 . 7 5 220 3.9 9 5 . 7 319.6 335.5 + l 5 . 9 4-1.5
++ ++
Variation of Volatilization of Potash with Temperature
Uniform samples consisting of 0.5 gram Wyomingite, 0.5 gram calcium carbonate, and 0.0752 gram, or 1 potash equivalent, of calcium chloride were heated for 40 minutes a t various temperatures. Table VI11 gives the results of these experiments. The agreement between calculated and actual losses in weight is very good, except for runs a t lower temperatures, 910" and 1010" C., where volatilization was small. It is likely that the large negative difference in runs 58 and 57 is due to the fact that a t lower temperatures the decomposition of calcium carbonate to lime and carbon dioxide was not complete, so that the actual loss in weight was smaller than the one calculated on the assumption that all the carbon dioxide left the crucible. In this series of experiments duplicates were made a t 1310°, 1410°, and 1510" C., as volatilization a t these temperatures appeared to be less than a t lower temperatures and it was thought advisable to check up these results.
Effect
IO
I
I1
%OD
300
of fernperdure on
volafilizaflon
of KzO from /euc!ik Mixiures a f 0 5 g /euofe, 0 5 9 CaCO, and one K20 eouivalenf of CaCI, were heated
20
fir 40
minufes
I IO00
JJOO
It00
/NO
Temperature
-
I400
ISGO
%GO
O c
Figure 7
Figure 7 shows the temperature-volatilization curve. At first volatilization is small-only 36.13 per cent a t 1010" C. Between 1010" and 1110" C. there is a sudden jump to 98.43 per cent. The curve stays up a t almost 100 per cent until 1210" C. is reached, then it comes down again slightly and stays down through the remaining temperature range. This behavior might be explained on the ground that when the crucible is introduced into the furnace a t lower temperatures the calcium chloride present volatilizes more slowly and therefore has a greater chance to react with the potash of the Wyomingite through a longer period. When the tem-
83
perature is near the boiling point of calcium chloride, which is 1500" C., this material volatilizes rapidly in the first few minutes, and little of it is left to react. It is likely that a t the lower temperatures of 910" and 1010" C. more of the potash has reacted with calcium chloride to form potassium chloride, but only a small amount, to the extent of 22.10 and 36.13 per cent, has volatilized. The analysis for residual potash might have included some potassium chloride which did not volatilize a t low temperatures. This assumption is confirmed by the work of Ross (b'), who found that, on heating 1 gram of feldspar with 1 gram of calcium carbonate and 0.25 gram calcium chloride a t 1000-1050" C. for 2 hours, 59.8 per cent of the potash in the feldspar was rendered soluble. Conclusions
Potassium can readily be removed from Wyomingite by volatilization by means of calcium carbonate and a halogen salt promoter. Calcium carbonate alone is not very effective in inducing volatilization. Using a ratio of Wyomingite to calcium carbonate of 1 to 2, the amount of potash volatilized was only 42.79 per cent. However, calcium carbonate is necessary to 5ux the silica in the myomingite, if this method of potash volatilization is to be applied in a smelting processfor instance, in a blast furnace. In that case the amount of calcium carbonate to be used will be governed by the amounts of alumina and silica in the Wyomingite, so that the resulting slag will have the proper fluidity. Of the halogen salt promoters calcium chloride is the most effective. This promoter should not be used in amount far above the potash equivalent in the Wyomingite. A mixture of Wyomingite and calcium carbonate in the ratio 1 to 1 and 1 potash equivalent of calcium chloride will give a volatilization of 95 to 98 per cent a t 1200-l50O0 C. in a short time. Any excess of calcium chloride will be volatilized and the gain in volatilization will be only a few per cent. Time is not an important factor in a smelting volatilization process of potash. Most of the potash will leave the Wyomingite in a short time, and any further heating will help little. With sodium and calcium chlorides as promoters it was found that in the first 10 minutes about 70 and 90 per cent of potash, respectively, left the crucible. It is true that these particular relations of time to volatilization are characteristic of the amount of material used, size of particles, and the design of the furnace. In a smelting process, such as in a blast furnace, where the material would be charged into the furnace in large lumps and where a large volume of gases would be blown through the material, the time effect might be different in degree, but not in the general trend. It seems to make little difference what the temperature is, provided it is above 1100" C. Although the experiments indicate that volatilization in the interval between 1110" and 1310" C. is slightly greater than between 1310" and 1510" C., the difference is only about 4 per cent. I n the reactions between potash of the Wyomingite and the various reagents studied there is in every case, theoretically, a certain amount of heat evolved, the amounts being 216, 349, 104, and 198 kilojoules, respectirely, for calcium carbonate, calcium chloride, sodium chloride. and calcium fluoride. This fact seems to indicate why the reactions whereby potash changes into potassium chloride, potassium fluoride, and potassium carbonate take place a t all, as a reaction will tend favorably in a direction of exothermicity. The study presented in this paper indicates that the method of volatilization of potash from Wyomingite by some smelting process is chemically feasible. The successful application of this method on a commercial scale mill depend on the proper design of a furnace. Experiments reported here
ISDUSTRIAL A N D ENGINEERIi$'G CHELVIISTRY
84
were undertaken to lay the foundation for the design of such a furnace. Acknowledgment
The writer wishes to express his thanks to J. JV, Turrentine suggestions given and Royster for many freely in connection with this work.
Vol. 23, No. 1
Literature Cited (1) Chance, J . SOL.Chem. I n d . , 37, 222-230 (1918). ( 2 ) Jackson and Morgan, J. IRD. EX. C H E M .15, , 110 (1921). (3) Jackson and Morgan, Ibid., l 5 292 ~ (lg2I). (4) Rhodin, J . SOC.Chem. I n d . , 20, 939 (1901). ( 5 ) Ross, 8th Intern. Cong. d p p l i e d Chem., 15, 217 (1912). (6) Wells, U. S. Geol. Survey, Prof. Paper 98-D,37-40 (1916)
Smelting of Wyomingite and Phosphate Rock in the Blast Furnace' T. P. Hignett and P. H. Royster FERTILIZER AHD F I X E DNITROGEN INVESTIGATIONS, BUREAUO F CHEMISTRY A N D SOILS,WASHINGTON, D. C .
The Bureau of Chemistry and Soils has made atthat is, the more than 65 per N IMPORTANT part tempts to smelt both phosphate rock and Wyomingite, of the work on fertilcent of the heat not usable with a view to recovery of soluble potash salts and phosizer technology a t the for phosphate reduction-all phates from the resulting fume. The results are quite goes to waste. As the hot Bureau of Chemistry and encouraging, volatilization of more than 90 per cent gas from the reduction zone Soils is concerned with the of both KnOand P206having been achieved. The volaascends the furnace shaft, it possibility of applying blasttilization of the PnOaseems to depend on high-temmust preheat the descending furnace technic to the properature heat, while volatilization of KzO is dependent charge and melt the slag. duction both of phosphoric on the addition of chlorides. I n many cases, however, the acid and of p o t a s h . I n a Rock Springs non-coking soft coal was investigated heat required for slagging the paper read before the AMERIas a possible blast-furnace fuel, with promising results. charge is considerably less CAN CHEMICAL SOCIETYa t Indications are that a commercial blast furnace operthan the shaft heat, and in Minneapolis, R o y s t e r and ating on Wyoming leucite, western phosphate rock, Turrentine described an atc on s e q u e n c e the over-all limestone, and Rock Springs coal should be able to prothermal efficiency of the proctempt to smelt p h o s p h a t e duce K 2 0 and PnOaat plant cost of 525 per ton. The ess is relatively low. rock in the bureau's experim e n t a l blast furnace. In product might suitably be in the concentrated form It was in an"effort to utilize spite of the small size of the of potassium phosphates. some of this waste shaft heat for the volatilization of potunit, no operating difficulties were encountered and the process appeared technically simple. ash that the experiments described in the present paper were The commercial success of the phosphate furnace was found undertaken. Some such process is uniquely applicable in to be a question solely of coke consumption, and this coke the Wyoming potash field, where high-grade phosphate rock consumption in its turn was found to be largely, if not exclu- is available both from Wyoming and from southern Idaho. Although in a strictly logical sense the potash produced in sively, a matter of preheating the blast. this process is a by-product of a phosphate furnace, economiUtilization of Shaft Heat cally the phosphoric acid is more nearly a by-product in Although the misused expression "volatilization of phos- the production of potash. I n smelting high-grade phosphate rock in any furnace it is phoric acid" is rather firmly fixed in the literature, in actual fact that PzOsin phosphate rock is not volatilized a t any at- necessary to add to the charge some form of siliceous material tainable furnace temperatures. The removal of P205in a as a flux. The use of a potash-bearing silicate for fluxing phosphate rock and recovering both phosphorus and potash has furnace can be accomplished only by the reduction of phosbeen suggested a number of times (1, t?,6 , B ) . Recently Pike phoric oxide to elementary phosphorus. This reduction re(4) has described the smelting of Idaho phosphate rock and action is strongly endothermic and does not take place with any great rapidity below 1300" C. I n a blast furnace blown Wyomingite in an experimental blast furnace. I n the present with air preheated to 750" C. gas is produced in the combus- experiments, however, the potash silicate was added to utilize tion zone a t about 2000" C. As it passes through the phos- the shaft waste heat, and the amount of silicate used in each phate charge this gas can supply the reduction reaction with case was more than enough to flux the phosphate rock, so heat only while its temperature is greater than 1300" C. I n that a further addition of limestone or burnt lime was necessary to flux the excess silica in the charge. I n other words, other words, only the fraction or 35 per cent a potash furnace was operated to smelt Wyomingite, and the of the heat, is available for reduction. By heating the blast lime contained in phosphate rock was used as a flux for the to a higher temperature the combustion-zone temperature silica in the charge up to the limit of the heat available for can be raised and the fraction of the heat usable in phosphate phosphate reduction and limestone was used for the rest of reduction can be increased. It is obvious, therefore, that the needed flux. any important reduction in the fuel consumption of the phosOperation of Experiment Blast Furnace phate furnace must come through an improvement in the dcThe blast furnace used in the experiment is shown in Figsign of the hot blast stoves. ure 1. It is 80 inches tall and has a hearth diameter of 13 It should not be thought that the so-called "shaft heat"inches, a bosh diameter of 19 inches, and a total volume of 12 1 Received September 22, 1930. Presented before the Division of cubic feet. For comparison a modern blast furnace is 90 Fertilizer Chemistry at the 80th Meeting of the American Chemical Society, feet tall, has a 25-foot hearth and a total volume of over Cincinnati, Ohio, September 8 t o 12, 1930
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